This invention relates to papermaker's wet press felts and more particularly to such a felt in which the opposite ends are joined by a pin seam.
The prior patent art contains numerous examples on pin-seam type felts for paper making machines, along with discussions of the advantages which can be gained by using pin-seam felt over a more conventional endless felt. These prior patents include the following U.S. Pat. Nos. and foreign patent documents:
Draper, Jr., 2,883,734 of Apr. 28, 1959 PA0 Kelleher, et al, 3,283,388 of Nov. 8, 1966 PA0 Codorniu, 3,815,645 of June 11, 1974 PA0 Cannon, 4,401,137 of Aug. 30, 1983 PA0 Lilja et al, 4,601,785 of July 22, 1986 PA0 Talonen et al, 4,698,250of Oct. 6, 1987 PA0 Johansson et al, 4,743,482 of May 10, 1988 PA0 Sakuma, 4,755,260 of July 5, 1988 PA0 Japanese patent 57-55358
Typically, the pin seam felt today is formed with a woven base fabric and carries one or more layers of needled batting material on one or both of the face surfaces of the base fabric. An advantage of the pin seam on such a felt is that the felt can be made as stiff as desired, and still get it threaded onto the paper making machine. If the same felt were woven endless, it would be very heavy, stiff, and difficult to install on the machine.
Difficulties are encountered in two general areas. The one of these difficulties resides in the necessity of threading the pin through the cross-machine fabric loops on the opposed ends of the felt. The ends of the felt must be brought together on the machine, and a flexible leader wire is threaded through the internested loops, a short section or length at a time. Then it is used to pull the pin through while Pulling the leader out of a gap between loops. This is repeated across the width of the machine, which may exceed 400 inches. The tedious process is often made all the more difficult because of cramped space and poor lighting.
A second difficulty resides in the necessity of cutting through the layer or layers of needled batting at the pin seam joint, since the joint was temporarily joined during felt manufacture and batt needling. Once the batting layer has been severed at the seam, it is very difficult to join it together again on the machine.
The above list of patent documents contains a number of examples of attempts to deal with this problem, including the Japanese publication, and the U.S. Pat. Nos. 4,764,417; 4,755,260; 4,743,482; 4,698,250; and 4,601,785. In several instances it has been suggested that the batting layer be cut on an oblique angle to the base fabric, or that it is cut along a line laterally offset from the seam, or both. In most cases, a flap of the batting layer is formed by the cut, and while the prior art talks in terms of securing -he flap, such as by gluing, the fact is that most such batting flaps run free in use, and can cause undesirable marking on the paper.